Highly pressurized carbon dioxide fluids such as liquid, gaseous, or supercritical CO2 (e.g., at or above 31° C. and 1,071 pounds per square inch gauge (psig)) are required for a variety of industrial processes. In certain instances, gaseous, liquefied, or supercritical carbon dioxide may be seen as a replacement for organic solvents or aqueous-based process solutions that are currently in use as cleaning or processing solutions.
Many cleaning or processing applications in the electronic industry may demand the use of carbon dioxide fluids at high flow rates and high pressures. One of the methods for achieving high pressure carbon dioxide has been to pump liquid carbon dioxide to a required pressure. However, pumping liquid carbon dioxide to a high pressure can introduce contaminants, such as particulates, hydrocarbons, halocarbons, etc., to the fluid stream.
Certain industries such as semiconductor manufacturing require high pressure carbon dioxide fluids delivered to a process tool or point of use (POU) at high or ultra high purity (UHP) levels, i.e., having low parts per million (ppm) or low parts per billion (ppb) of contaminants. Small quantities of contaminants are detrimental to the microchip fabrication process in the manufacturing of semiconductor electronic components. Contaminants, in the form of particulates, films, or molecules, can cause a variety of defects, such as short circuits, open circuits, and silicon crystal stacking faults. These defects can cause the failure of the finished component, such as integrated circuits, and these failures can cause significant yield reductions, which greatly increases manufacturing costs. Because of this, cleaning is the most frequently repeated step in the manufacture of integrated circuits. At the 0.18-micrometer design rule, 80 of the approximately 400 total processing steps in the manufacture of an integrated circuit are typically cleaning steps. Substrates typically are cleaned after every contaminating process step and before each high temperature operation to ensure the quality of the integrated circuit.
Semiconductor-applications can generally produce a range of contaminants. Contaminants may be introduced into the carbon dioxide fluid from many sources such as residues from manufacturing process steps such as lithography, etching, stripping, and chemical mechanical planarization (CMP); particulates either indigenous to and/or resulting from manufacturing processes; inorganic particulates or materials such as native or chemical oxides, metal-containing compounds; and contaminants introduced from manufacturing equipment such as pumps, compressors, or other sources. These contaminants can have a vapor pressure either above or below that of carbon dioxide. Higher vapor pressure contaminants may be, for example, fluorine, lower molecular weight fluorinated hydrocarbons, or atmospheric gases such as nitrogen and oxygen. Certain contaminants such as, for example, photoresist residue may be difficult to remove from the carbon dioxide fluid because they are non-volatile.
Current market demands of UHP carbon dioxide fluids are satisfied using cylinder supply and represent a limited development activity for semiconductor manufacturers. However, as semiconductor manufacturers increasingly adopt UHP carbon dioxide as a replacement for aqueous-based process solutions, larger scale or bulk CO2 supply systems will be needed. Typical bulk CO2 supply systems, that are used to deliver and store CO2 in other industries, such as food manufacturing, are operated at a pressure of about 300 psia and temperature varying from about −15° F. to 2° F. or −26° C. to −17° C. Further, these industries do not necessarily require a high or an ultra-high purity (UHP) product. The semiconductor industry, by contrast, require UHP CO2 delivered to the POU or process tool used in processes such as photo-resist removal, deposition, lithography, etc., at significantly higher pressures. The required product pressure at these process tools could vary from 2,000 psig to 10,000 psig. Pressure requirements depend on many factors such as application specifics, tool design, process philosophy, etc.
The semiconductor industry faces significant technical challenges developing the onsite systems that will handle UHP CO2 from bulk sources to process tools. Some of these challenges include, but are not limited to, storage of UHP CO2 in large quantities at high pressures; purity maintenance along the onsite UHP CO2 handling system; liquid product delivery via long pipelines; and liquid product delivery to POU at pressures above 900 psig.